Along with continual progress of the semiconductor fabrication process, popularity of the Internet, emergence of information appliances, and usage of wireless communications and broadband networks, the life information age comes into being. Transmission of information becomes faster and more diversified. In order to meet the requirements for information of people, the wireless communications technology has become the star attentively looked at by everybody. The requirement for wireless products has also increased relatively.
For a common wireless communications product, its transceiver mainly comprises a receiver and a transmitter. The present invention aims to innovate the transmitter. As shown in FIG. 1, a conventional transmitter comprises a shift register 10, wherein data is shifted therein according to a shift signal after data is loaded, and a 3-bit data signal is outputted to an address generator 12. After the address generator 12 generates a valid address according to index of a sample index counter 14, a corresponding sine baseband modulation signal is acquired from a lookup table in a read-only memory (ROM) 16. The sine baseband modulation signal is then stored in a locker 18. The address generator 12 uses the same way to acquire a corresponding cosine baseband modulation signal, which is then stored in a locker 20.
When both the sine baseband modulation signal and the cosine baseband modulation signal are obtained, the two locker 18 and 20 simultaneously trigger signals to make use of digital-to-analog converters (DACs) 22 and 24 to convert the sine baseband modulation signal and the cosine baseband modulation signal into a sine analog modulation signal. (Q signal) and a cosine analog modulation signal (I signal), respectively. The Q signal is transmitted to a low-pass filter 26 for filtering, and the I signal is transmitted to another low-pass filter 28 for filtering. Next, a frequency synthesizer 30 is used to modulate the two signals to an emission frequency to become a radio-frequency (RF) signal for emission.
The lookup table in the ROM 16 stores baseband modulation signals. In addition to the receiver's frequency synthesizer, the transmitter requires another frequency synthesizer 30 of the emission frequency to modulate the baseband signals to the emission frequency. Because the transmitter requires another frequency synthesizer 30, the structural complexity is raised, the volume cannot be shrunk, and the difficulty in manufacturing is also increased.
Accordingly, the present invention aims to propose a wireless transmitter to effectively resolve the problems in the prior art.